Apparatus for rotatably suspending a pipe string in a well

ABSTRACT

An apparatus for rotatably suspending a pipe string in a well includes a rotating member, a stationary member, and a bearing assembly. The bearing assembly is mounted in a chamber defined by the rotating and stationary members and is interposed between axially spaced and transversely extending bearing surfaces formed, respectively, in the stationary and rotating members. The bearing assembly includes a plastic ring positioned in the chamber to engage one of the bearing surfaces and two concentric metal rings positioned in the chamber to substantially cover the other bearing surface. The engagement of the plastic ring on the metal rings is such to force the metal rings radially apart and against opposite interior surfaces of the chamber as thrust loads are applied to the apparatus.

United States Patent 1 1 Heilhecker et al. 1 1March 13, 1973 [54]APPARATUS FOR ROTATABLY 3,555,006 10 1970 Orkin et al. ..308/238SUSPENDING A IPE TRING N A 3,602,560 8/1971 Memmel ..308/238 WELL P E .lA L k I n in [75] Inventors: Joe K. Heilhecker, Bellaire; William z z igg sz :35; et a1 app C. Maurer, Houston, both of Tex.

[73] Assignee: Esso Production Research Company, [57] ABS CT Houston Anapparatus for rotatably suspending a pipe string in [22] Filed: Aug. 25,1971 a well includes a rotating member, a stationary member, and abearing assembly. The hearing as- [211 Appl' 174533 sembly is mounted ina chamber defined by the rotating and stationary members and isinterposed between [52] U.S. Cl. ..166/208, 308/135, 308/238 axiallyspaced and transversely extending bearing sur- [51] Int. Cl. ..E2lb43/10 faces formed, respectively, in the stationary and rotat- Field 0fSearch ing members. The bearing assembly includes a plastic 0 ringpositioned in the chamber to engage one ofthe bearing surfaces and twoconcentric metal rings posi- [56] Re erences Cited tioned in the chamberto substantially cover the other bearing surface. The engagement of theplastic ring on UNITED STATES PATENTS the metal rings is such to forcethe metal rings radially 3,578,828 5/1971 Orkin et al. ..308/135 apartand against opposite interior surfaces of the 2,218,783 10/1940 Bernhard308/ 164 chamber as thrust loads are applied to the apparatus. 2,842,9457/1958 Swanson ..308/l35 3,424,503 1/1060 Schulz ..308/238 17 Claims, 4Drawing Figures L l S 20 23 12 \l 2 2l g a2 '53 26 4g 34 s s 22- s s s QZ I, I

PATENIEDMAR13|9I5 SHEET 10F 2 INVENTORS JOE K. HEILHECKER WILLIAM C.MAURER BY ATTORNEY PATENTEDmmmm 51 SHEETEUFZY FIG. 3

INVENTORS JOE K. HE/LHECKER WILLIAM C. MAURER APPARATUS FOR ROTATABLYSUSPENDING A PIPE STRING IN A WELL BACKGROUND OF THE INVENTION 1. Fieldof the Invention This invention relates to an improved pipe hangingapparatus usable in well completion operations.

2. Description of the Prior Art In completing an oil well, gas well,water well, or similar borehole, it is customary to case the well withheavy steel pipe and provide a cement sheath about the outer peripheryof the pipe. The cement sheath adds strength to the pipe string,protects the metal from corrosion, and prevents migration of fluidsbetween subsurface formations. For the cement to be effective, it isessential that it substantially surrounds the pipe string. Placement ofthe cement about the pipe normally involves positioning the pipe stringin the wellbore and pumping a cement slurry down through the pipe stringand up the wellbore annulus. The cement slurry displaces the drillingmud ahead of it. Because of the relatively high gel strength of mostdrilling muds, complete displacement of the drilling mud by the cementslurry is difficult to achieve, particularly with long pipe strings.Experience has shown that the cement slurry tends to channel through thedrilling mud, resulting in a nonu niform cement sheath about the pipestring. One approach for improving the displacement operation involves atechnique wherein the pipe is rotated as the cement slurry is pumpedthrough the pipe string and up the well bore annulus. Tests have shownthat pipe rotation improves mud displacement in two important respects:it breaks the gel structure of the mud and it eliminates stagnantpockets of mud in the wellbore annulus. For wells drilled on land,rotation can be achieved by suspending the casing on the drilling swiveland applying torque to the casing by the rotary table. For offshorewells drilled with floating vessels, however, use of the swivel tosuspend the pipe is not possible because of vessel motion. Vessel motionrequires that the casing be suspended on the subsea wellhead assembly.The radial space for accommodating the casing hanger in most subseaassemblies is limited. This limited bowl space does not providesufficient radial clearance to permit the use of rolling-elementbearings having sufficient load carrying capacity to support the casingstring. The cementing of such pipe strings is thus generally performedwithout the known benefits of pipe rotation. As previously noted, thissubstantially increases the risk of obtaining a poor cement job.

Another application where pipe rotation is desirable is in linerinstallations. A liner is a pipe string suspended within an existingcasing string in the wellbore. It is normally employed where it is notnecessary for the inner pipe to extend to the surface. Considerablesavings in pipe cost can be realized by suspending the liner within alower portion of the outer casing string. Rotating liner hangers arecommercially available and normally include a ball bearing for carryingthrust loads. Such assemblies, because of their limited load carryingcapacity, are normally used to set relatively short lengths of liners.This somewhat limits the utility of rotating liner hangers because, aspreviously noted, the mud displacement problem is particularly seriousin long pipe strings.

SUMMARY OF THE INVENTION The improved apparatus constructed according tothe present invention can be used in connection with casing hangers,liner hangers, or other applications where it is desired to rotatablysupport a pipe string in a well. Briefly, the apparatus includes astationary member, a rotatable member, and a bearing assembly forcarrying thrust loads. As applied in connection with pipe hangingassemblies, the stationary member is designed to be secured to thewellhead assembly or outer casing, and the rotatable member is designedto carry the pipe string to be cemented in the borehole. When assembled,the stationary member and rotatable member define a substantiallyenclosed chamber which contains the thrust bearing assembly. The thrustbearing assembly comprises two rings composed of relatively soft bearingmetal such as copper or bronze alloys and a plastic ring having arelatively low coefficient of friction. The bearing assembly ispositioned within the chamber in such a manner that the plastic ringengages one of the members, e.g., rotating member, and the two metalrings arranged in concentric relation substantially cover the gapbetween the two members to prevent excessive extrusion of the plasticring. The metal rings preferably are sized in relation to each other toprovide a relatively small clearance therebetween. The plastic ringengages both metal rings and is shaped in relation to the confrontingsurfaces of the metal rings to provide a radial component of force oneach metal ring as load is applied to the assembly. Applied load, thus,tends to force the metal rings apart into sealing engagement with thechamber walls.

The surface of the member engaging the metal rings preferably is facedwith a hard, wear-resistant material such as one of thenickel-chromium-boron alloys.

The thrust bearing assembly requires substantially less radial mountingspace than that required for rolling-element bearings of comparable loadcarrying capacity. Pipe hangers provided with the bearings assembly canbe readily suspended in subsea assemblies as well as within casingstrings and permit rotation of substantially longer pipe strings thereinthan previously possible. Tests have shown that the apparatus of thepresent invention can support thrust pressures as high as 10,900 psi forseveral hours with no. noticeable deterioration of the bearings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic view, shownpartially in longitudinal section, of a portion of a subsea wellassembly illustrating the apparatus in connection with casing hangers.

FIG. 2 is an enlarged, fragmentary view of the apparatus shown in FIG. 1showing details of the improved apparatus.

FIG. 3 is a longitudinal sectional view of a portion of a cased wellboreillustrating the apparatus in connection with a liner hanger.

FIG. 4 is an elevational view, shown in longitudinal section, of a testrig employing the support apparatus of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For purposes of illustration,the present invention will be described in connection with a casinghanger and a liner hanger. It should be emphasized, however, that theimproved apparatus can be used in other applications where it is desiredto rotatably suspend a pipe string in a well.

Depending upon pipe diameter, pipe location, and pipe use, pipe stringsare referred to in the art as drilled pipe, casing, tubing, or liners.As used herein, the terms pipe or pipe string embrace the wide varietyof conduits commonly used in the drilling, completion, and repair ofwells.

Considering first the embodiment in connection with casing hangers, FIG.1 schematically illustrates a subsea wellhead assembly for a floatingdrilling vessel. The assembly comprises a guide structure resting on theocean floor, a surface pipe string 1 1, and a hanger mandrel 12. Thesurface pipe string 11 is suspended on the guide structure 10 and iscemented in place. The hanger mandrel 12 has a cone section 13 whichmates with an internal shoulder, or bowl, 14 secured to the surface pipe11. The mandrel 12 serves several functions: it provides means forsupporting components of the subsea assembly which include a hydraulicconnector, illustrated as 15, blowout preventors, marine conductor pipe,and similar equipment; it also provides a support base for suspendingpipe strings installed during the drilling of the well. In deep wells,the mandrel 12 will normally provide support for several casing strings.For example, one common design calls for 30 inch diameter surface pipe,three intermediate casing strings of inch diameter, 13% inch diameter,and 9% inch diameter, and a production string of 7 inches in diameter.Thus, it is seen that FIG. 1 is somewhat simplified in that only thesurface pipe string 11, intermediate pipe string 16, and a productionstring 17 are shown. Cementing of the intermediate pipe strings whichare relatively short in relation to the production string 17, normallyis not difficult to achieve because the relatively large annulus betweenthe casing and the borehole favors mud displacement by the cementslurry. The production string 17, on the other hand, is extremelydifficult to cement because of the mud displacement problems describedearlier. Factors which promote cement channeling through the mud includesmall clearance between the casing and borehole, relatively long lengthsof pipe, and the eccentric location of the pipe string in the borehole.These factors coupled with the gel characteristics of the mud make itextremely difficult to obtain a competent cement sheath about theproduction string. It has long been known that pipe rotation duringcementing operation improves the displacement mechanism. The rotatingpipe breaks the gel structure of the mud and eliminates stagnant pocketsin the annulus. As mentioned earlier, rotation of long pipe stringssuspended from floating vessels has not been possible, heretofore,because of vessel motion. Moreover, the limited bowl space in subseawellhead assemblies precludes the use of conventional bearings. Asillustrated in FIG. 1, the casing hanger must be sufficiently small topass through the upper components of the subsea assembly and to lodge inthe mandrel l2.

A feature of the apparatus of the present invention is that it requiresrelatively small radial mounting space and therefore can readily bemounted in the mandrel 12.

The apparatus shown generally as 18, includes a stationary member 19, arotating member 20, and a bearing assembly 21. The rotating member 20 isadapted to carry the pipe string 17 whereas the stationary member 19 isadapted to seat in the mandrel bowl. The bearing assembly 21 permitsrelative rotation of the members 18 and 19 as torque is applied to therunning-in string at the surface.

Referring to FIG. 2, the rotating member 20 is seen to include a tubularbody portion 22 and a flanged portion 23 which extends radiallyoutwardly from body portion 22. The axial opening through the apparatusshould have a diameter about the same as the casing string 17 suspendedtherebelow. Formed in the flanged portion 23 is a downwardly openingannular groove sized to receive bearing 21 and associated components.The bearing 21 comprises a three ring assembly including a plastic ring25 and two metal rings 26 and 27. The plastic ring 25 fits into theupper portion of the groove and engages a downwardly facing bearingsurface of member 20. The two rings. 26 and 27 arranged concentricallyin the groove define an upper surface shaped complementary to the lowersurface of plastic ring 25 The stationary member in this embodimentcomprises two parts, washer 28 and retainer 29. The washer 28 is sizedto fit into the groove and therein provides an upwardly facing bearingsurface. The three ring bearing assembly 21 and washer 28 are maintainedwithin the groove by the retainer 29. In a sense then the washer 28 androtating member 20 cooperate to define a substantially enclosed chamberhaving confronting axially spaced and transversely disposed bearingsurfaces. The plastic ring 25 is adapted to bear against one of thebearing surfaces and the concentric rings 26 and 27 against the other.The retainer 29 bears against the bottom surface of the washer 28 andhas a lower flanged portion 30 adapted to seat in the bowl or matingsurface 31 formed in the mandrel 12. Several radial flow channels, twoshown as 35 and 36, formed in the bottom surface of flange 30 permitdrilling mud to flow around the apparatus during cementing operations.

The rings 26 and 27 are arranged in side-by-side, concentric relation inthe groove and each has a downwardly facing surface engaging the topsurface of the washer 28 and a radially facing surface confronting awall of the groove. The inner surface of ring 26 confronts an outersurface of ring 27 along an interface (shown as line 24 in FIG. 2). Theclearance between the rings 26 and 27 along interface 24 should besufficient to permit relative rotational movement of the rings 26 and27. This clearance can vary within relatively wide limits depending onthe size of the rings 26 and 27, pressure imposed on the apparatus, andmaterials employed. Preferably, the clearance should be such to providea sliding fit between the rings 26 and 27, e.g., clearance less than 5mils; preferably between 0 and 2 mils.

Upper surfaces 32 and 33 of rings 26 and 27, respectively, can betapered as illustrated. These surfaces mate with the lower complementaryshaped surface of plastic ring 25. As thrust loads are applied to theassembly, the mating relationship of ring 25 on surfaces 32 and 33results in a radial component of force on each of the bearing rings 26and 27. The outer ring 26 is forced into abutting engagement with theouter confining surface of the groove and the inner ring is forced intoabutting engagement with the inner surface of the groove. The rings 26and 27 thus substantially cover the radial spaces between the washer 28and the walls of the groove and prevent excessive extrusion of theplastic ring 25. It should be observed that the specific configurationsof the rings 25, 26, and 27 can be other than that disclosed. Theseconfigurations, however, must be such to force the concentric ringsapart in response to axial thrust loads on the apparatus 18.

The bearing rings 26 and 27 can be made of any metal bearing material.Preferably, the bearing material is of intermediate compressivestrength. The hardness and modulus of elasticity of these materialsshould generally be as low as possible and yet provide sufficientstrength to carry the applied load. Preferred bearing materials includebronze, leaded bronze, tin bronze, phosphor bronze, as well ascopper-lead alloys and similar bearing materials. These materials arerelatively soft having a Brinnell hardness less than 100 and arelatively low modulus of elasticity.

The bearing rings 26 and 27 can be machined to the proper dimensions byconventional techniques. The size of the rings 26 and 27 should be suchthat they can be assembled in concentric relation and inserted into thegroove. The clearance between each ring and the wall of the groovenormally will be between about 2 and 6 mils to permit easy installation.

The plastic ring 25 occupies substantially all of the space of thegroove above the bearing rings 26 and 27. The plastic ring can be moldedfrom most any dry bearing plastic, the most popular of which includesnylon polycarbonates, acetals and the fluoroplastics. Thefluoroplastics, particularly polytetrafluoroethylene, are

vpreferred because of their low coefficient of friction,

high temperature resistance, and good lubricating qualities. Theseplastic materials can be molded into the desired configuration by knownmolding techniques. As indicated above, the top and outer surfaces ofthe plastic ring 25 are shaped complementary to the confining walls ofthe groove and the bottom surface is shaped complementary to the topsurface defined by the assembled rings 26 and 27.

As mentioned previously, the washer 28 should be faced with a hard,wear-resistant surface. A steel core faced with nickel-chromium-boronalloy has proven satisfactory for this service. The alloy sold under thetrade name Colmonoy provides a highly polished, hard, wear-resistantsurface. Other hard facing materials include high chromium iron, cobaltchromium alloy, and copper base alloys. The nickel-chromium-boron alloysare preferred, however, because they are highly wear resistant, andretain their hardness at elevated temperatures.

The installation of the apparatus 18 when applied in connection withcasing hangers can be performed as follows. When the well has beendrilled to the proper depth, the drill string is withdrawn from thewellbore and a casing string denoted 17 in FIG. 1 is lowered into thehold by conventional techniques. The apparatus 18 comprising rotatablemember 20, bearing assembly 21,

and the stationary member (washer 28 and retainer 29) is secured to thetop joint of the casing string 17. The retainer 29 may be held in placeby mechanical means such as a plurality of shear pins, two shown as 34in FIG. 2, extending radially through the flange 23 and having inner endportions protruding into suitable recesses formed in retainer 29. Theapparatus 18con nected to the casing string 17 is lowered to the propersetting location on a pipe string 37 of the same diameter as casing 17.This assembly is run into the hole until the retainer flange 30 seats onthe mandrelbowl surface 31. This transfers the weight of the casing 17to the mandrel 12. Initial torque applied to the string 37 at thesurface causes the pins 34 to shear, permitting rotation of member 20 onthe stationary portion of the apparatus. The thrust loads applied on thebearing assembly cause the plastic ring 25 to deform and substantiallyconform to the shape of the upper extremity .of the chamber. The plasticmaterial thus acts much in the manner of the viscous fluid applying ahydraulic force on the bearing rings 26 and 27 forcing them apart intoengagement with their respective chamber walls. En gagement of thebearing rings 26 and 27 on the chamber walls prevents excessive axialextrusion of the plastic material between the rings 26 and 27 and thewalls of the groove.

Although it is not clear which of the rings 25, 26 and 27 remainstationary and which rotate, the wear pattern on test assembliesindicate that part of the time the outer ring 26 remains stationaryandthat the plastic ring 25 and inner ring 27 rotate. The plasticmaterial tends to extrude at a slow rate between the rings 26 and 27 andthe groove walls and along interface 24 provid ing lubrication for thesliding surfaces. The extruding plastic also provides lubrication forthe sliding surfaces between washer 28 and ring 26 and/or ring 27.

During pipe rotation, cement can be pumped through the running-in pipestring 37, the casing 17 and up the wellbore annulus displacing drillingmud ahead of it. The drilling mud flows through the channels 35 and 36in the retainer flange 30 and to the surface. After the cement has beenplaced, the running-in pipe string 37 can be disconnected from therotating member 20 and retrieved. In some applications it may benecessary to run a packer to seal the annulus above the flange 23 toclose off the flow channels 35 and 36.

Another embodiment of the invention is disclosed in connection with aliner hanger, shown in FIG. 3. A liner is generally installed in lieu ofa complete casing string in order to save on material cost. Liners arenormally duspended in a lower portion of an existing casing and cementedin place. A liner hanger attached to the top of the liner is required inorder to secure the assembly to the existing casing. Although rotatingliner hangers have been used in the past, their limited load carryingcapacity has restricted their use to relatively short liners. Theapparatus of the present invention permits the suspension of relativelylong liners.

The liner hanger 40 comprises a rotating head 41, a stationary member42, a bearing assembly shown generally as 43, and a slip assembly 44.The upper end of the head 41 is adapted to be connected to a runninginstring 45, e.g., tubing, drill pipe, etc., and the lower end is adaptedto be connected to a liner 46. The 'running-in string 45 may alsoinclude a setting tool (not shown) which functions to collapse packersafter the cementing operation is completed.

The rotating head 41 includes a tubular body portion 47 and a flange 48which extends radially outwardly from the body 47. The inside diameterof the head 41 is preferably the same as that of the liner 46. Theflange 47 has formed therein an annular, downwardly opening groove sizedto receive the three ring bearing assembly 43, which is generally thesame construction as previously described, having a plastic ring and twometal rings. Because of the space limitations between the liner 46 andexisting casing shown as 49, the bearing assembly 43 used in linerhangers probably will be somewhat smaller in radial dimension than thebearing assembly used in casing hangers described previously.

The bearing assembly 43 bears against a washer 50 which closes thegroove opening. The washer 50 has an upper bearing surface engaging thebottom surface of the bearing assembly 43 and preferably is faced with ahard, wear-resistant material such as a nickel-chromium-boron alloy. Thewasher 50 and bearing assembly 43 are maintained within the groove bytop surface of a slip expander cone 51. The cone 51 extendscircumferentially around the tubular portion 47 and is sized in relationthereto to permit free rotation of the two members. A stop collar 52secured to the tubular portion 47 maintains the cone 51 in place duringrunning-in operations. The slip assembly 44 includes a plurality ofgripping jaws 53. Each gripping jaw 53 is riveted or otherwise connectedto a spring member 54 which is an extension of a bow spring 55. The bowsprings 55 are shaped to frictionally engage the well casing 49. Duringrunning-in operations, the gripping jaws 53 are maintained in aretracted position below the cone 51. At the proper setting depth thejaws 53 are released by reciprocation of the pipe or by hydraulic actiondepending upon the mechanism employed. Lowering of the pipe then causesthe jaws 53 to be wedged between the casing 49 and cone 51 asillustrated in FIG. 3.

In operation, the liner 46 and hanger 40 are lowered into the casedwellbore on a running-in pipe string 45 which as previously noted caninclude a setting tool of conventional construction. At the propersetting depth, the slip assembly 44 is actuated, causing the slip jaws53 to be wedged between the cone and the casing. This transfers the loadof the liner 46 and running-in assembly to the stationary portion of thehanger, e.g., washer 50, cone 51, and slip jaws 53 which are, in turn,supported on the well casing 49. As cement is pumped from the surfacethrough the running-in string 45, the hanger 40, the liner 46, and upthe casing-liner annulus, the pipe string is rotated by applying torqueat the surface. The drilling mud displaced by the cement flows up theannulus passing around the liner hanger 40. Following the cementingoperations, the running-in string is disengaged from the liner hanger 40and retrieved. The liner hanger 40 constructed according to the presentinvention, because of the increased load carrying capacity of thebearing assembly 43, is capable of supporting substantially longerliners than are commercially available liner hangers.

The following laboratory experiment illustrates the effectiveness of theapparatus of the present invention. A test assembly shown in FIG. 4 wasconstructed. The assembly included a steel head member 61 having adownwardly opening groove formed therein. The groove had an outsidediameter of 3.533 inches and a thickness of 0.721 inches. A bearingassembly comprising a plastic ring 62 of polytetrafluoroethylene and twobearing rings 63 and 64 of phosphor bronze (SAE 660 were placed in thegroove; The polytetrafluoroethylene ring 62 was 3.529 inches in outsidediameter, 0.713 inches thick, and 0.375 inches in height (from tip tobase). The inside and outside diameters of the inner ring 63 were 2.816and 3.173 inches, respectively, and the inside and outside diameters ofthe outer rings 64 were 3.173 and 3.529 inches, respectively. The rings63 and 64 were 0.250 inches in height and had upper, inwardly taperingshoulders which defined an included angle of 110. A washer 65 faced withColmonoy hard, wear-resistantalloy was inserted in the groove. Thewasher 65 had inside and outside diameters of 2.817

and 3.528 inches, respectively, and a height of 0.310

inches. The head 61 and bearing assembly were placed on the upper end ofa short joint of pipe 66. The pipe bolted to a base had inside andoutside diameters of about 2.85 and 3.50 inches, respectively. A radialbearing 67 having an inner race secured to the pipe 66 and an outer racesecured to the head 51 maintained the pipe 66 and groove in axialalignment. The head 61 was connected to a hydraulic press, a portionshown as joint 68. The test apparatus included a rotary table forrotating joint 68 and a torque transducer for measuring the appliedtorque. A load of 40,000 pounds was applied to the head 61 as theassembly was rotated at 20 rpm. The 40,000 load resulted in a pressureof about 10,900 psi on the thrust bearing. The initial torque requiredto maintain 20 rpm was about 280 foot-pounds. After 3% hours, the testwas discontinued for 10 minutes. When the test was resumed at sameoperating conditions, the torque required to rotate the assembly at 20rpm with applied load of 40,000 pounds was initially about 550foot-pounds. The torque leveled off to about 350 footpounds in about 2minutes and then, after about 10 minutes, increased to about 380foot-pounds. The test was discontinued. The test apparatus wasdisassembled. The plastic ring 62 and bearing rings 63 and 64 were intact and showed very little wear. The following morning, the test wasresumed and continued for 3% additional hours. During the final 25minutes, the torque was somewhat erratic, increasing to about 700footpounds at one point and 600 foot-pounds at another. At theconclusion of the test, however, the assembly was rotating smoothly atan average torque of about 430 foot-pounds. Following the test, the testapparatus was disassembled. The plastic ring 62 had split along ahorizontal plane near the base of the tapered portion.

The lower bearing surface of outer ring 64 was badly pitted whereas thecorresponding surface of inner ring 63 showed no evidence of pitting.The outer periphery of ring 64 was worn indicating relative motionbetween that ring and the wall of the groove. The inner surface tion bythe plastic between the outer periphery of ring 64 and the groove wall.There was also evidence of plastic lubrication between the bottomsurface of ring '64 and washer 65.

. clearly understood. It: is believed, however, that the lubricationprovided by the plastic material extruding between sliding surfacesplays a major role. The radial component of force on the rings 63 and 64forcing them apart appears to prevent excessive axial extrusion of theplastic materiaL-This force also causes the rings 63 and 64 to conformto the walls of the groove thereby compensating for wear.

Although the improved apparatus has been described mainly in connectionwith casing and liner hangers, it again should be emphasized that theinvention can be applied equally well in other applications where it isdesired to rotatably suspend a pipe string in awell.

We claim:

1. An apparatus for rotatably suspending a pipe string in a well whichcomprises a stationary member adapted to be secured to a supportingstructure for said well; a rotating member adapted to be connected tosaid pipe string, said stationary and rotating members in combinationdefining an annular chamber therebetween including two axially spacedand transversely disposed bearing surfaces; two concentric rings ofbearing metal substantially covering one of said surfaces; and a plasticring between said concentric rings and the other of said surfaces, theengagement of said plastic ring on each of said concentric rings beingsuch to force said concentric rings apart and against the interior ofsaid chamber in response to axial thrust on said apparatus.

2. The apparatus as defined in claim 1 wherein said concentric rings aresized to enable relative sliding movement therebetween.

3. The apparatus as defined in claim 2 wherein said concentric rings aresized to provide a radial clearance therebetween of less than about 5mils.

4. The apparatus as defined in claim 2 wherein said concentric rings aresized in relation to each other to provide a radial clearancetherebetween of from 0 to 2 mils. y

5. The apparatus as defined in claim 2 wherein said one surface is facedwith a hard-facing alloy.

6. The apparatus as defined in claim 1 wherein said bearing rings arecomposed of a bearing metal having a Brinnell hardness less than about100.

7. The apparatus as defined in claim 6 wherein said bearing metal is abronze alloy.

8. The apparatus as defined in claim 1 wherein said plastic material isa fluoroplastic.

9. The apparatus as defined in claim 5 wherein said fluoroplastic ispolytetrafluoroethylene.

10. A pipe hanger for rotatably suspending a pipe string from asupporting structure in a well which comprises: a stationary supportmember adapted to be secured to said supporting structure; a rotatingmember adapted to suspend said pipe string, one of said members havingan annular glroove formed therein and the other of said members avmg anannular end portion positioned in said groove, said groove and said endportion presenting axially spaced and transversely disposed surfaces; abearing assembly mounted in said groove between said surfaces andincluding a plastic ring and two concentric metal rings positioned insaid groove to substantially cover the radial spaces between said endportion and the inner and other walls of the groove to prevent excessiveextrusion of the plastic ring.

11. The pipe hanger as defined in claim 10 wherein said metal rings arecomposed of a bearing metal having a Brinnell hardness less than about100.

12. The pipe hanger as defined in claim 10 wherein said plastic ring iscomposed of a fluoroplastic.

13. The pipe hanger as defined in claim 12 wherein the fluoroplastic ispolytetrafluoroethylene.

14. The pipe hanger as defined in claim 10 wherein said metal rings aresized to provide a radial clearance therebetween of less than about 5mils.

15. The pipe hanger as defined in claim 14 wherein said radial clearanceis between 0 and about 2 mils.

16. The pipe hanger as defined in claim 10 wherein said end portionpositioned in said groove is faced with a hard-facing alloy.

17. An apparatus for rotatably suspending a liner in a case bore whichcomprises: a stationary member having an axial opening formed therein;means for securing said stationary member to the interior of the wellcasing; a rotatable member having a tubular portion extending throughsaid opening formed in said stationary member, the lower end of saidtubular portion being adapted to be connected to said liner, and aflanged portion having a downwardly opening, annular groove formedtherein, said stationary member having an upper end portion disposed insaid groove; a plastic ring mounted in said groove above said endportion; and two concentric metal bearing rings positioned in saidgroove to substantially cover the radial space between said end portionand the walls of said groove to prevent excessive extrusion of saidplastic ring.

1. An apparatus for rotatably suspending a pipe string in a well whichcomprises a stationary member adapted to be secured to a supportingstructure for said well; a rotating member adapted to be connected tosaid pipe string, said stationary and rotating members in combinationdefining an annular chamber therebetween including two axially spacedand transversely disposed bearing surfaces; two concentric rings ofbearing metal substantially covering one of said surfaces; and a plasticring between said concentric rings and the other of said surfaces, theengagement of said plastic ring on each of said concentric rings beingsuch to force said concentric rings apart and against the interior ofsaid chamber in response to axial thrust on said apparatus.
 1. Anapparatus for rotatably suspending a pipe string in a well whichcomprises a stationary member adapted to be secured to a supportingstructure for said well; a rotating member adapted to be connected tosaid pipe string, said stationary and rotating members in combinationdefining an annular chamber therebetween including two axially spacedand transversely disposed bearing surfaces; two concentric rings ofbearing metal substantially covering one of said surfaces; and a plasticring between said concentric rings and the other of said surfaces, theengagement of said plastic ring on each of said concentric rings beingsuch to force said concentric rings apart and against the interior ofsaid chamber in response to axial thrust on said apparatus.
 2. Theapparatus as defined in claim 1 wherein said concentric rings are sizedto enable relative sliding movement therebetween.
 3. The apparatus asdefined in claim 2 wherein said concentric rings are sized to provide aradial clearance therebetween of less than about 5 mils.
 4. Theapparatus as defined in claim 2 wherein said concentric rings are sizedin relation to each other to provide a radial clearance therebetween offrom 0 to 2 mils.
 5. The apparatus as defined in claim 2 wherein saidone surface is faced with a hard-facing alloy.
 6. The apparatus asdefined in claim 1 wherein said bearing rings are composed of a bearingmetal having a Brinnell hardness less than about
 100. 7. The apparatusas defined in claim 6 wherein said bearing metal is a bronze alloy. 8.The apparatus as defined in claim 1 wherein said plastic material is afluoroplastic.
 9. The apparatus as defined in claim 5 wherein saidfluoroplastic is polytetrafluoroethylene.
 10. A pipe hanger forrotatably suspending a pipe string from a supporting structure in a wellwhich comprises: a stationary support member adapted to be secured tosaid supporting structure; a rotating member adapted to suspend saidpipe string, one of said members having an annular groove formedtherein, and the other of said members having an annular end portionpositioned in said groove, said groove and said end portion presentingaxially spaced and transversely disposed surfaces; a bearing assemblymounted in said groove between said surfaces and including a plasticring and two concentric metal rings positioned in said groove tosubstantially cover the radial spaces between said end portion and theinner and other walls of the groove to prevent excessive extrusion ofthe plastic ring.
 11. The pipe hanger as defined in claim 10 whereinsaid metal rings are composed of a bearing metal having a Brinnellhardness less than about
 100. 12. The pipe hanger as defined in claim 10wherein said plastic ring is composed of a fluoroplastic.
 13. The pipehanger as defined in claim 12 wherein the fluoroplastic ispolytetrafluoroethylene.
 14. The pipe hanger as defined in claim 10wherein said metal rings are sized to provide a radial clearancetherebetween of less than about 5 mils.
 15. The pipe hanger as definedin claim 14 wherein said radial clearance is between 0 and about 2 mils.16. The pipe hanger as defined in claim 10 wherein said end portionpositioned in said groove is faced with a hard-facing alloy.